This invention relates to a mechanism for transmitting power from a driving side to a driven side. For example, the invention relates to a power transmission mechanism which is provided with a buffer having a predetermined buffering characteristic by interposing a buffer member such as rubber or a spring member between the driven side which is a magnet rotor shaft for rotating a heavy rotor such as electric generator and the driving side which is a generator idly fitted onto this rotor shaft.
For example, referring to FIG. 1, in a power transmission mechanism for a motorcycle or the like, the power of an engine 1 is transmitted to a gear 5 at the side of a speed change gear by way of a gear 3 and a chain 4 from a crank shaft 2. Reference numeral 6 denotes a flywheel. In this case, a force is generated by which the vehicle body is swung right and left as the rotation of the engine becomes high or low in what is called "an engine of a longitudinally set type" in which the crank shaft 2 is arranged in the forward and rearward direction of the vehicle body. Stated differently, as the engine is abruptly accelerated or decelerated, the angular acceleration component of rotation increases, thereby causing a torque of inertia which swings the vehicle body right and left. It has been known to rotate the magnet rotor shaft 8 of the generator 7 in a direction opposite to that of the crank shaft 2 by means of a pair of gears 9, 10 for driving the generator, to null this force.
There is also in the art an anti-torque balancer. Specifically, a driving gear 3 is directly coupled to the crank shaft 2. A driven gear 10 is directly coupled to the rotor shaft 8 of the generator 7 having a large moment of inertia. Both of the gears are made to engage each other so that the rotor shaft 8 of the generator 7 may rotate in a direction which is opposite to that of the crank shaft 2, thereby generating an inertia torque in a direction which is opposite to an inertia torque of the crank shaft 2 on the rotor shaft 8 of the generator.
However, the gas pressure functions on an engine piston must also be considered. It varies by a large margin in correspondence with each stroke. Accordingly, an inertia force in a reciprocating part in an internal combustion engine is created and a periodical torque variance is caused. Consequently, forced torsional oscillation power is developed by this variance of torque.
A vibration component, noise and the like, for example, due to the collision between the gears which is attributable to the engagement of the gears or the like is apt to be created in the middle and high speed rotation regimes of the engine because the rotor shaft 8 which is relatively heavy is rotated by means of the gears 9 and 10. Then, the rotation of the gear 10 is transmitted to the rotor shaft 8, for example, by way of buffer members 11 made of an elastic member such as coiled spring, rubber or the like (FIG. 2). However, the variance in the speed is apt to be created in the low speed rotation regime. Also, circumferential slippage between the gear 10 and the gear shaft 8 frequently occurs, so that the gear 10 resonates to develop vibration or noise which also becomes a problem.
If the torsional oscillation frequency of the crank shaft coincides with, or approaches, a characteristic frequency which is determined by the moment of inertia of the rotor shaft system of the generator 7 and the composite spring constant of this rotor shaft 8 and the spring, resonance is caused, thereby making it impossible to achieve the buffering action.
Furthermore, the torque of inertia in the system of the rotor shaft 8 of the generator is small when the crank shaft is rotating at a low speed. Conversely, since the variance in the rotation speed of the crank shaft, that is, the angular acceleration of the crank shaft 2 is relatively large, if the above-mentioned buffer is operative, the variance in the rotation speed of the crank shaft is absorbed by the buffer, so that the torque of inertia of the crank shaft is nulled by the rotor of the generator. This makes it impossible to effectively perform the essential function of the anti-torque balancer to prevent vibration of the vehicle body.